docs: def usage(self):
          """
          Provide output of `s2i usage`
  
          :return: str
          """
          c = self._s2i_command(["usage", self.get_full_name()])
          with open(os.devnull, "w") as fd:
              process = subprocess.Popen(c, stdout=fd, stderr=subprocess.PIPE)
              _, output = process.communicate()
              retcode = process.poll()
          if retcode:
              raise ConuException("`s2i usage` failed: %s" % output)
          return output.decode("utf-8").strip()